The present invention relates to a plastics additives powder composition, a process for preparing the same, thermoplastic resin blends containing the same, and methods of improving the impact properties and enhancing processability of thermoplastics. These compositions and processes provide plastics additive powders having excellent powder flow properties that provide a combination of superior impact strength and processability to thermoplastic resins, especially polyvinyl chloride.
Thermoplastic resins ordinarily require various additives for modifying their processing and/or property characteristics. Examples of such additives for plastics include: dyes and pigments for altering color; thermal stabilizers and antioxidants for reducing degradation and coloring during processing, high temperature use, and/or long-term weathering; fillers for reducing cost and/or increasing rigidity; lubricants for improving processability and reducing sticking to machine surfaces; antistatic agents for reducing build up of static charge in plastic parts; plasticizers for increasing plasticity and flexibility; impact modifiers (xe2x80x9cIMxe2x80x9d) for improving impact strength to reduce part breakage; and high polymer processing aids (xe2x80x9cprocessing aidsxe2x80x9d, xe2x80x9cPAxe2x80x9d) for controlling the rheological characteristics for optimizing resin processability and increasing process efficiency.
During the preparation of thermoplastic resin blends and plastic part fabrication, the various additives are usually added as separate powdered, pelletized, or liquid components to the thermoplastic resin. Because thermoplastic blend formulation usually requires one to handle many materials having varied physical properties, preparation of these blends is both costly and complex. (Generally, see xe2x80x9cPlastics Additives and Modifiers Handbookxe2x80x9d J. Edenbaum, Ed., Van Nostrand Rein, 1992 for discussion of various additives for plastics.)
It is therefore desirable to obtain compositions of plastics additives that not only reduce cost but also reduce the complexity of preparing fully formulated thermoplastic resin blends. It is also desirable to obtain compositions of plastics additives that provide further improvements to the physical use properties as well as the processability of fully formulated thermoplastic resin blends.
Impact modifiers for thermoplastic resins are rubber-containing particles, typically having diameters in the range of from 50 to 1000 nm, which are dispersed throughout the thermoplastic resin. Conventionally, these impact modifiers include at least one rubbery polymer particle surrounded by at least one hard polymer shell and are prepared using emulsion polymerization techniques. The rubbery polymer portion is believed to enable the thermoplastic matrix resin to absorb physical shocks, prevent crack initiation, and prevent crack propagation in plastic parts, resulting in reduced breakage and increased impact strength. For high impact efficiency the mean particle size of the impact modifier should generally be greater than 100 nm. Such rubbery polymers are conventionally based on units derived from ethylenically unsaturated monomers that provide glass transition temperatures (xe2x80x9cTgxe2x80x9d) below 25xc2x0 C. Examples of monomers that provide rubbery polymers include butadiene, isoprene, C1-C8 alkyl acrylates, alpha-olefins, ethylenically unsaturated siloxanes and ethers, and copolymers of mixtures thereof.
Because polymer particles tend to be sticky and not isolatable as a dry powder, a hard polymer shell is typically added to the exterior of each rubbery xe2x80x9ccorexe2x80x9d particle in order to prepare impact modifiers as dry powders that are easily handled. The hard polymer shells of impact modifiers are ordinarily selected to be compatible with the thermoplastic resin so that the impact modifier (xe2x80x9cIMxe2x80x9d) disperses readily into the thermoplastic resin during compounding. The hard polymer shells are usually derived from vinyl aromatic (e.g., styrene), methacrylic (e.g., methyl methacrylate), and acrylonitrile monomers. Often, graftlinking agents are added to either the rubbery or hard polymer phases to increase the strength of attachment of the shell to the core.
Generally, as the rubbery weight fraction of an IM increases, the required amount of IM in the thermoplastic formulation decreases. The amount of impact modifiers in a thermoplastic resin formulation varies with the type of resin and application, but is generally between 3 and 30 parts based on 100 parts thermoplastic resin (xe2x80x9cphrxe2x80x9d). In creating xe2x80x9cefficientxe2x80x9d impact modifiers, therefore, the weight fraction of the rubbery core in the IM is typically maximized. However, it has been conventionally known that if the rubbery core fraction is too high then the hard shell polymer is not able to completely cover the rubbery core, thereby resulting in poor powder properties and dispersibility. Depending on the monomers used, the maximum core:shell weight ratio in powdered impact modifiers has conventionally been about 88:12. It is therefore desirable to increase the rubbery weight fraction in impact modifiers for plastics which have good powder properties and disperse readily in thermoplastic resins using conventional equipment.
Processing aids for thermoplastic resins are typically polymers and copolymers containing units polymerized from ethylenically unsaturated monomers such as vinyl aromatic, (meth)acrylonitrile, and/or C1-C4 alkyl methacrylate monomers. Processing aids are typically prepared using emulsion polymerization techniques to yield dispersions of 20-500 nm mean diameter hard polymer particles having a molecular weight in the range of from at least 50,000 to greater than 5,000,000 g/mol and a Tg greater than 25xc2x0 C. The processing aid particle dispersions are typically dried and isolated to form a free-flowing powder, the powder particles having a 50-500 micron mean diameter. This PA powder is subsequently added to thermoplastic resin formulations.
The amount of PA used in a thermoplastic resin formulation varies with the type of resin and application, but is generally between 1 and 15 phr. Processing aids are commonly compatible with the thermoplastic resin. For example, processing aids based on polymers and copolymers prepared with methyl methacrylate (xe2x80x9cMMAxe2x80x9d) monomer which have a molecular weight greater than 1,000,000 g/mol are commonly added to PVC resin formulations to promote quick fusion (melting), and thereby increasing process efficiency, of the PVC resin. Processing aids are also useful in increasing the melt strength of thermoplastic resins, which is important during certain types of process applications, such as during foaming and thermoforming of molten thermoplastic resin blend formulations.
U.S. Pat. No. 5,442,012 describes encapsulated plastics additives containing both impact modifier and flow improving (processing aid) particles for modifying the impact properties and processing characteristics of PVC and thermoplastic matrix polymers. Both impact modifier and processing aid particles are prepared separately at particle sizes less than 100 nm by emulsion polymerization, co-micro-agglomerated at temperatures above 70xc2x0 C., and subsequently encapsulated by a final shell polymer. Although the encapsulated shell polymer allows for the isolation of the impact modifier having acceptable flow properties, its presence dilutes the concentration and effectiveness of the impact modifier and processing aid components in the encapsulated plastics additives. Moreover, the impact modifying efficiencies afforded by these plastics additives are limited because the impact modifier particles must have a particle size below 100 nm. As a result, using these encapsulated plastics additive powders in PVC provide similar, but not improved, impact strength and processing characteristics compared to using equal amounts of separate impact modifier and processing aids.
The present inventors have discovered new plastics additives powders and processes for preparing these powders that overcome the shortcomings of U.S. Pat. No. 5,442,012. The present inventors have discovered new plastics additives powder compositions that combine the functionality of a high rubber IM with the functionality of a PA without requiring an encapsulating shell and without requiring that the mean particle size of the IM and PA is less than 100 nm diameter. The plastics additives of the present invention further provide improved, impact strength and processing characteristics compared to using equal amounts of separate impact modifier and processing aids in PVC formulations. Enhanced impact strength results by providing plastic additive powders containing IM particles having rubber contents exceeding 88% by weight of the IM, while excellent powder properties and processing aid functionality are provided by the method of coagulating these high rubber IM particles with PA particles. As a result, the plastics additives of the present invention provide thermoplastic resin formulators with: (1) ease of use in handling one powdery additive rather than two (both an IM and a PA); (2) reduced costs by allowing less total plastics additives to be used; and (3) improved impact properties as powdery impact modifiers containing greater than 88% rubber are now possible.
The plastics additives powder compositions of the present invention are provided as powder particles having IM particles and first and second PA polymer particles. When blended in thermoplastic resins such as PVC, the IM polymer particles increase the impact strength and the PA polymer particles improve process efficiency and melt strength. Unexpectedly, we have found that the impact and processing properties achieved by the particular compositions of the present invention are more efficient and/or provide performance improvements compared to using the separate IM and PA powders. The PA particles also function to affect the preparation of high rubber IM polymer particles having rubber weight fractions greater than 88% as a free-flowing powder. Moreover, the PA particles further function to increase the dispersibility of such high rubber soft polymer particles in thermoplastic resins.
In a first aspect of the present invention, there is provided a plastics additives powder composition providing a combination of impact modifying and processing characteristics in thermoplastic resins, the composition comprising:
(a) from 50 to 98 parts by weight of impact modifier particles, the impact modifier particles having a mean particle size greater than 100 nm;
(b) from 0 to 48 parts by weight of first processing aid particles; and
(c) from 2 to 50 parts by weight of second processing aid particles, wherein the composition of the second processing aid particles is the same as, or different than, the composition of the first processing aid particles,
wherein the total parts by weight of the impact modifier particles, the first processing aid particles, and the second processing aid particles is equal to 100.
In as second aspect of the present invention, there is provided a plastics additives powder composition providing a combination of impact modifying and processing characteristics in thermoplastic resins, the composition comprising:
(a) from 82 to 93 parts by weight of impact modifier particles having a mean particle size greater than 100 nm, the impact modifier particles comprising from 89 to 94 parts by weight of at least one rubbery polymer, and 6 to 11 parts by weight of at least one hard polymer;
(b) from 5 to 10 parts by weight of first processing aid particles having a mean particle size greater than 100 nm, the first processing aid particles having a molecular weight greater than 1,000,000 g/mol; and
(c) from 2 to 8 parts by weight of second processing aid particles having a mean particle size greater than 100 nm, the second processing aid particles having a molecular weight greater than 1,000,000 g/mol,
wherein the composition of the second processing aid particles is the same as, or different than, the composition of the first processing aid particles,
wherein the total parts by weight of the impact modifier particles, the first processing aid particles, and the second processing aid particles is equal to 100.
In a third aspect of the present invention, there is provided a method for preparing a plastics additives powder providing a combination of impact modifying and processing characteristics in thermoplastic resins, the method comprising the steps of:
(a) preparing a first aqueous particle dispersion comprising:
(i) from 50 to 98 parts by weight of impact modifier particles, the impact modifier particles having a mean particle size greater than 100 nm, and
(ii) from 0 to 48 parts by weight of first processing aid particles;
(b) coagulating the first aqueous particle dispersion to form a coagulated slurry;
(c) adding a second aqueous particle dispersion to the coagulated slurry, the second aqueous particle dispersion comprising,
from 2 to 50 parts by weight of second processing aid particles, wherein the composition of the second processing aid particles is the same as, or different than, the composition of the first processing aid particles, and
wherein the total parts by weight of the impact modifier particles, the first processing aid particles, and the second processing aid particles is equal to 100; and
(d) drying the coagulated slurry to less than 5 weight percent water to form a free-flowing powder.
In a fourth aspect of the present invention, there is provided a method for preparing a plastics additives powder providing a combination of impact modifying and processing characteristics in thermoplastic resins, the method comprising the steps of:
(a) preparing a first aqueous particle dispersion comprising:
(i) from 50 to 98 parts by weight of impact modifier particles, the impact modifier particles having a mean particle size greater than 100 nm, and
(ii) from 0 to 48 parts by weight of first processing aid particles;
(b) coagulating the first aqueous particle dispersion to form a coagulated slurry;
(c) drying the coagulated slurry to form a wetcake;
(d) adding a second aqueous particle dispersion to the wetcake, the second aqueous particle dispersion comprising,
from 2 to 50 parts by weight of second processing aid particles, wherein the composition of the second processing aid particles is the same as, or different than, the composition of the first processing aid particles, and
wherein the total parts by weight of the impact modifier particles, the first processing aid particles, and the second processing aid particles is equal to 100; and
(e) drying the wetcake to less than 5 weight percent water to form a free-flowing powder.
In a fifth aspect of the present invention, there is provided a thermoplastic resin blend, comprising: (A) a thermoplastic resin, and (B) a plastics additives powder composition according to the first aspect of the present invention; wherein the weight ratio of (A):(B) is in the range of from 1:99 to 99:1.
In a sixth aspect of the present invention there is provided a method of modifying a thermoplastic resin, comprising: (I) melt blending the thermoplastic resin blend of the fourth aspect of the present invention.
As used herein, the term C1 to C12 alkyl (meth)acrylate refers to the class of compounds containing the alkyl esters of methacrylic acid or acrylic acid, wherein the alkyl esters have from one to twelve carbon atoms.
As used herein, the term (meth)acrylonitrile refers to the compounds acrylonitrile and methacrylonitrile.
As used herein, the term xe2x80x9cpartsxe2x80x9d refers to parts by weight.
As used herein, the term xe2x80x9cmean particle sizexe2x80x9d refers to the mean diameter of polymer particles.
All ranges disclosed herein are inclusive and combinable.
The following abbreviations are used herein: ALMA=ally methacrylate; BA=butyl acrylate; BMA=butyl methacrylate; EA=ethyl acrylate; IM=impact modifier; MMA=methyl methacrylate; N2=nitrogen; PA=processing aid; PD=particle dispersion; p.s.=particle size; SFS=sodium formaldehyde sulfoxylate; SLS=sodium lauryl sulfate; SPS=sodium persulfate; tBHP=t-butyl hydroperoxide; DALMA=diallyl maleate; DIW=deionized water; DSC=differential scanning calorimetry; GPC=gel permeation chromatography; Mw=weight average molecular weight.
The plastics additives powder composition of the present invention provides a combination of impact modifying and processing characteristics in thermoplastic resins. The composition of the present invention contains: from 50 to 98, preferably from 75 to 96, most preferably from 82 to 93 parts by weight of IM particles; from 0 to 48, preferably from 3 to 18, most preferably from 5 to 10 parts by weight of first PA particles; and from 2 to 50, preferably from 2 to 18, most preferably from 2 to 8 parts by weight of second PA particles. In the present invention, the second PA particles are the same as, or different than, the first PA particles. In the plastics additives of the present invention, the total parts by weight of the IM particles, the first PA particles, and the second PA particles is equal to 100.
The IM particles of the present invention comprise from 80 to 100, preferably from 88 to 96, most preferably from 89 to 94 parts by weight of at least one rubbery polymer, and from 0 to 20, preferably from 4 to 12, most preferably from 6 to 11 parts by weight of at least one hard polymer. The total parts by weight of rubbery and hard polymers is equal to 100.
The IM particles are readily prepared according to the art of core/shell emulsion polymerization to provide one or more IM particles having a mean particle size greater than or equal to 100 nm, preferably in the range of from 100 to 500 nm, and more preferably in the range of from 100 to 300 nm. Preparation of acrylic core/shell impact modifiers are readily prepared according to the teachings in U.S. Pat. Nos. 3,859,389 and 5,612,413.
The rubbery polymers of the IM particles are preferably in the form of a spherical core particle, although it is possible for the IM to have rubbery domains. The rubbery polymers comprise polymerized units derived from one or more ethylenically unsaturated monomers, wherein the glass transition temperature of the at least one rubbery polymer is less than 25xc2x0 C., preferably less than 0xc2x0 C., most preferably less than xe2x88x9240xc2x0 C. Such rubbery polymers can be prepared from polymerized units derived from one or more ethylenically unsaturated monomers known in the impact modifier are, such as alkyl acrylates, 1,3-dienes, vinyl acetate, siloxanes, alpha-olefins, and mixtures thereof.
In the IM particles, for reasons of cost and efficacy it is preferred that the C1 to C12 alkyl (meth)acrylates in the core polymer is BA. Such core polymers can include homopolymers of BA, copolymers of BA with other acrylates, such as ethyl acrylate, 2-ethylhexyl acrylate and the like, copolymers with monomers of higher refractive index, such as styrene and the like, copolymers with (meth)acrylonitrile and the like. The molecular weight of the core polymers of the IM particles may be controlled by use of chain transfer agents, such as alkyl mercaptans.
For best impact properties, it is preferred that the rubbery polymer, especially if formed from an acrylate monomer such as BA or 2-ethylhexyl acrylate, further contains 0.1 to 5 parts by weight of units derived from at least one multiunsaturated monomer, such as at least one of ALMA, allyl acrylate, DALMA, diallyl fumarate divinylbenzene, a di- or triacrylate ester of a polyol, or a di- or trimethacrylate ester of a polyol, and the like to function as a rubbery crosslinker and/or graft linker to the hard polymer.
The at least one hard polymer of the IM is composed of at least one domain that has preferably a shell-like morphology, and most preferably a shell-like morphology disposed externally to, and grafted to the rubbery polymer. It is preferred that the IM particles further comprise from 0.01 to 5 weight percent of one or more multi-ethylenically unsaturated units so that at least 80 weight percent of the at least one hard polymer is grafted to the rubbery polymer.
The IM may contain additional shells between, or external to, the rubbery polymer and hard polymer domains. Such additional shells, if present, can further be derived from particular monomers, such as styrene, for improvement of refractive index, as long as the other requirements of the first core/shell polymer are met.
The first and second PA particles are prepared according to the art of emulsion polymerization (e.g., U.S. Pat. No. 3,833,686) to provide one or more PA particles having a mean particle size in the range of from 20 to 500 nm, preferably from 70 to 300 nm, and most preferably from 100 to 300 nm. The first PA particles and second PA particles can each include single-stage, two-stage, and/or multi-stage polymer particles, as well as core/shell polymer particles.
The first and second PA particles each are comprised of polymerized units derived from one or more ethylenically unsaturated monomers. The preferred monomers include those selected from vinyl aromatics, butadiene, C1-C8 alkyl (meth)acrylates, (meth)acrylonitriles, and mixtures thereof. It is particularly preferred that the processing aids contain at least 50, preferably 75 parts by weight methyl methacrylate copolymerized with up to 50, preferably up to 25 parts by weight one or more C1-C12 alkyl (meth)acrylates, styrene, (meth)acrylonitrile, and mixtures thereof.
In the present invention, the first and second processing aids have a xe2x80x9chardxe2x80x9d polymer having glass transition temperatures measured by DSC of at least 25xc2x0 C., preferably at least 50xc2x0 C. The Mw of the xe2x80x9chardxe2x80x9d polymer of each PA are preferably greater than 100,000 g/mol, and more preferably greater than 1,000,000 g/mol. In certain thermoplastic formulations applications, such as PVC foam, it is desirable that the molecular weight of the PA is greater than 4,000,000 g/mol. In the case of two-stage or multistage core/shell polymer particles, it is preferred that the outer or shell polymer is such a xe2x80x9chardxe2x80x9d polymer.
The xe2x80x9chardxe2x80x9d polymers of the first and second processing aids may also be formed from homo- or copolymers of monomers such as styrene, methyl methacrylate, BA, ethyl acrylate, and the like, especially when the particle is prepared as a single-stage polymer particle. Although it is preferred that the processing aid polymers contain no crosslinker, the polymers may contain one or more units derived from multifunctional monomers containing two or more double bonds, such as from about 0.1 to about 5% of at least one of ALMA, allyl acrylate, DALMA, diallyl fumarate, divinylbenzene, a di- or triacrylate ester of a polyol, or a di- or trimethacrylate ester of a polyol.
In order for the plastics additive to have good compatibility with many thermoplastic matrix resins, such as PVC, it is preferred that the hard polymer domains (e.g., shells) of both of the IM and the first and second processing aids contain a majority of units derived from MMA. It is more preferred that the hard polymer domains of the IM contain more than 90% by weight MMA units and that the hard polymer domains of the first and second processing aids contain less than 90% by weight MMA units. For example, the hard polymer domains of the IM may contain a homopolymer of methyl methacrylate, or copolymers of methyl methacrylate with up to about 50%, preferably up to about 20%, of at least one co-monomer such as ethyl acrylate, BA, 2-ethylhexyl acrylate, butyl methacrylate, styrene, acrylonitrile, and the like.
Various surfactants known in the emulsion polymerization art can be used in preparing the particle dispersions used in the present invention. Surfactants include, but are not limited to, alkali metal or ammonium salts of long-chain alkylsulfonic acids, long-chain alkylsulfates, derivatives of aromatic sulfonates, ethoxylated alyaryl phosphates, fatty acids. Examples include sodium lauryl sulfate, sodium dodecylbenzene sulfonate, potassium dodecylbenzene sulfonate, lauryl(ethoxy)sulfates and sulfonates, lauryl(polyethoxy)sulfates and sulfonates, alkaryl(polyethoxy)sulfates and sulfonates, and the like.
The IM particles and the first and second PA particles are each provided as particle dispersions. Methods of preparing such particle dispersions for the methods of the present invention are best obtained by latex emulsion polymerization techniques as known in the emulsion polymerization art. The preferred IM dispersions and first and second PA dispersions were described earlier.
In the method for preparing the plastics additives powder of the present invention, the first step involves preparing a first aqueous particle dispersion. The first aqueous particle dispersion is prepared by combining, mixing, or blending from 50 to 98, preferably from 80 to 95, most preferably from 85 to 90 parts by weight of IM particles, and from 0 to 48, preferably 3 to 18, and most preferably 5 to 10 parts by weight of first PA particles.
The first aqueous particle dispersion has a percent solids weight fraction in the range of from 2% to 70%, preferably from 5% to 60%, and most preferably from 10% to 50%. These percent solids weight fraction ranges can be achieved by blending the IM and first PA particle dispersions each having the desired solids weight fraction, or having the desired weight fraction when combined. Accordingly, the solids weight fractions of each IM and PA particle dispersion is in the range of from 2% to 70%, preferably from 5% to 60%, and most preferably from 10% to 50%. In addition, the IM and first PA polymer dispersions can be prepared at particularly high percent solids weight fraction and subsequently diluted to achieve a preferred lower percent solids weight fraction. It is also possible to dilute the first aqueous particle dispersion to achieve a preferred lower percent solids concentration for the subsequent coagulation step. The first aqueous particle dispersion may also contain up to 5 parts by weight of a dispersion of flow aid polymer particles, such as those described in U.S. Pat. No. 4,463,131.
The first aqueous particle dispersion is subsequently coagulated to form a coagulated slurry. The coagulation step can be carried out by various coagulation methods known in the art, such as aqueous electrolyte (salt) coagulation using an aqueous solution of a salt of an inorganic acid, such as sodium chloride, magnesium acetate, calcium hypophosphite. It is preferred that the electrolyte solution is prepared with a salt containing a divalent cation, such as calcium chloride (CaCl2). Coagulation with a water soluble, or partially water soluble solvent, such as methanol and the like (xe2x80x9cmethanol-coagulationxe2x80x9d) is also possible. It is preferred to coagulate the first aqueous particle dispersion using aqueous electrolyte coagulation wherein the aqueous electrolyte solution has a concentration of between 0.1 and 2.0, preferably from 0.2 to 1.0 weight percent. It is also important to control the coagulation temperature because too high a coagulation temperature results in excessively large particles causing poor dispersion. In contrast, too low a temperature results in excessively small particles resulting in a wide particle size span and excessive dust. Coagulation temperature varies with the latex composition, particle size, emulsifier type, and pH. For example, when the first aqueous particle dispersion contain acrylic-based IM polymer particles having greater than 88% rubber, the coagulation temperature is in the range of from 0xc2x0 C. to 45xc2x0 C., preferably in the range from 0xc2x0 C. to 200C. In contrast, when the first aqueous particle dispersion contain acrylic-based IM polymer particles having less than 88% rubber, the coagulation temperature can be as high as 85xc2x0 C., but preferably less than 70xc2x0 C. The resulting coagulated slurry should have a percent solids weight fraction in the range of from 1% to 60%, preferably from 5% to 40%, and most preferably from 5% to 20%.
The second aqueous particle dispersion is subsequently added to the coagulated slurry. The composition of the second PA particles was described earlier, and can be different in composition than the composition of the first PA particles, but it is preferred that the compositions are the same. The second aqueous particle dispersion adds from 2 to 50, preferably from 2 to 18, and most preferably from 2 to 8 parts by weight of second PA particles to the coagulated slurry. The amount of second aqueous particle dispersion added to the coagulated slurry is determined by providing that the total parts by weight of the IM particles, the first PA particles, and the second PA particles is equal to 100.
The second aqueous particle dispersion should have a percent solids weight fraction in the range of from 2% to 70%, preferably from 5% to 60%, and most preferably from 10% to 50%. These percent solids weight fraction ranges can be achieved by preparing the second PA particle dispersion by emulsion polymerization having the desired percent solids weight fraction. It is also possible to dilute the second aqueous particle dispersion to achieve a preferred lower percent solids concentration.
In the present invention it is desirable that the second PA particles, when added to the coagulated slurry, subsequently coagulate onto the coagulated slurry particles. Some of the second PA particles may also coagulate separately among the coagulated slurry particles, but this should be minimized to avoid dust in the final plastics additive powder. This subsequent coagulation of the second PA particles onto the coagulated slurry particles of the IM and first PA particles is controlled by the temperature and electrolyte concentration in the coagulated slurry. The electrolyte concentration should be in the range of 0.1% to 2.0%, preferably 0.2% to 1.0%, most preferably 0.4% to 0.6%. When the rubber content of the IM is greater than 88%, the temperature of the second aqueous particle dispersion when added to the coagulated slurry should be controlled so that the resulting mixture has a temperature in the range of from 0xc2x0 C. to 45xc2x0 C., preferably in the range from 0xc2x0 C. to 20xc2x0 C. Higher coagulation temperatures may be used when the IM rubber content is less than or equal to 88%.
After adding the second PA particles it is desirable to ensure that the second PA particles are completely coagulated in the resulting coagulated slurry. This may be accomplished by subsequently adding additional electrolyte having a concentration in the range of from 5% to 40%, preferably 10% to 40%, most preferably from 20% to 40%. Higher concentration electrolyte solutions are preferred as it is desirable to minimize the amount of excess water added in the process just prior to the drying step.
After adding the second PA particles it is also desirable to ensure that the resulting coagulated slurry forms a free flowing powder having good compaction properties after it is dried. This can be accomplished by heating the resulting coagulated slurry to a temperature of at least 85xc2x0 C., preferably at least 95xc2x0 C., prior to drying.
After the step of adding the second aqueous particle dispersion according the process described, the resulting coagulated slurry should have a percent solids weight fraction in the range of from 1% to 60%, preferably from 5% to 40%, and most preferably from 5% to 20%. The resulting coagulated slurry has a mean slurry particle size in the range of from 150 to 400 microns, preferably 200 to 300 microns, and most preferably 200 to 250 microns. It is also desirable that the slurry particle size distribution is narrow to avoid the presence of dust from very small particles and the presence of undesirably large slurry particles that disperse poorly in thermoplastics resins. The particle size distribution span (xe2x80x9cspanxe2x80x9d) is defined as:   span  =                    d        90            -              d        10                    d      50      
wherein dx is the particle diameter in the particle size distribution below which x%, based on volume, of the total particles reside in the distribution. The resulting coagulated slurry of the plastics additives of the present invention has a span less than 3.0, preferably less than 2.0, and most preferably less than 1.5. It is also possible to separate out undesirably large slurry particles using various methods known in the art, such as filtration.
The resulting coagulated slurry is dried to less than 5 weight percent water to form a free-flowing powder. Various methods of drying particle slurries are readily known to those skilled in the art and are described in Chemical Engineer""s Handbook, 5th Ed., Perry and Chilton, Eds. 1973 which relates to the drying of solid-liquid particle dispersions. The preferred drying methods include fluidized bed dryers, rotary dryers, spray dryers, continuous or batch tray dryers, flash dryers, and pneumatic conveying dryers. During the drying step it is important to control the drying temperature so that the slurry particles do not fuse among themselves, for example by keeping the temperature of the slurry particles below the Tg of the hard polymer components (e.g., outer shells) of the individual IM and/or first and second PA polymer particles. If the drying temperature is too high then the individual polymer particles may fuse together in the powder particles which may hinder their subsequent dispersion into thermoplastic matrices. A free-flowing, low-dust plastics additives powder is achieved when the water content is less than 5%, preferably less than 3%, most preferably less than 1%.
Although it is preferred that the drying step occurs after forming the resulting coagulated slurry, it is also possible to simultaneously perform the steps of adding the second aqueous particle dispersion to the coagulated slurry and drying the resulting coagulated slurry. This is desirable for the purposes of providing overall efficient process economy.
The drying step may proceed in one step, or in multiple steps. Multiple step drying can be used to remove a sufficient amount of water from the resulting coagulated slurry to form a wetcake, the wetcake preferably having less than 60 weight percent water. In this case one could first form a wetcake prior to subsequent drying wherein additional plastic additive components are added to the wetcake prior to final drying into a powdery product. Wetcake can be prepared according to methods known in the art, for example by filtration of the slurry using a vacuum filter belt, a centrifuge, a Buchner funnel, and the like.
Several other embodiments of the method of the present invention are also possible. One variation involves drying the coagulated slurry to less than 50 weight percent water to form a wetcake and subsequently or simultaneously adding the second aqueous particle dispersion to the wetcake, followed by drying to a free-flowing, low-dust plastics additives powder as described above.
Another variation of the present invention includes adding one or more other known plastic additive compositions, in either powder or aqueous form. These additives can be blended into the composition after the final coagulation step or formation of wetcake using standard equipment such as high-speed mixers, blenders, kneaders, extruders, fluidized drying beds, and the like. Other ingredients typically blended in thermoplastic formulations, such as lubricants, thermal stabilizers, waxes, dyes, pigments, fillers, and the like, may each have an aqueous solution, liquid, powdered, or pellet form, and may also be included in the present invention using this mixing equipment.
The plastics additive powders of the present invention may be used in various ways, including preparation of thermoplastic resin blends. The thermoplastic resin blends of the present invention contain a thermoplastic resin and a plastics additives powder of the present invention, wherein the weight ratio of the additive to the resin is in the range of from 1:99 to 99:1. These blends are readily prepared by melt-blending methods that are known in the art of plastics processing. For example, the plastics additive powders of the present invention can be blended with thermoplastic resin powders or pellets and melt processed using an extruder.
The thermoplastic resin blends of the present invention are especially useful as impact-modified thermoplastics when the weight ratio of additive to resin is in the range of from 3:97 to 30:70. The thermoplastic resin blends of the present invention can also be blended with higher amounts of the plastics additives powders of the present invention for preparing concentrated pellets of the plastics additive powders of the present invention.
The thermoplastic resin blends of the present invention may also be formed into pellets by the steps of blending, extruding and pelletizing using conventional plastics processing equipment. Such pellets may readily contain the plastics additive powders of the present invention and one or more thermoplastic resins in the weight ratio of additive to resin can be in the range of from 10:90 to 80:20.
The thermoplastic resin blends of the present invention have many uses, including calendered sheet, thermoformed sheet, injection molded articles, blow-molded articles, extruded articles, and the like. When the component monomers of the plastics additive are added in a way that the refractive indices are carefully matched to the thermoplastic resin, the resulting polymers are useful in applications requiring transparency.
The plastics additives of the present invention are preferably blended into poly(vinyl chloride) (xe2x80x9cPVCxe2x80x9d) and chlorinated PVC (xe2x80x9cCPVCxe2x80x9d) to improve impact strength and processability. The plastics additives of the present invention are especially useful for manufacturing PVC siding, window profiles, and other exterior building products where both efficient processing, impact strength, and weatherability of the PVC product are needed. The plastics additive is useful for preparing PVC siding when the first and second processing aids are present in the range of from 5 to 20 parts be weight in the plastics additive, and the plastics additive is present in the PVC formulation in the range of from 4 to 20 phr.
The plastics additive powders of the present invention are also envisioned to be useful for preparing PVC foam when the first and second processing aids are present in the range of from 25 to 50 parts be weight in the plastics additive powder.
The plastics additives may be blended into many thermoplastics other than PVC, including thermoplastics based on polymers and copolymers of alkyl (meth) methacrylate, vinyl aromatics (e.g., styrene), and/or (meth)acrylonitrile, aromatic polyesters such as poly(ethylene terephthalate) or poly(butylene terephthalate), polycarbonates, polyamides, polyacetals, and polyolefins. The plastics additives may be admixed with various blends and alloys of one or more of these thermoplastic resins. The utility of such blends is varied, but include equipment panels and housings, such as for appliances or computers and automobile parts such as door panels and bumpers.